JPS6344837B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Fields> The present invention provides a corrosion-resistant material that has a beautiful plating color tone, excellent adhesion, is suitable as a base for painting, and has excellent overall rust prevention including painting. The present invention relates to a method for manufacturing a Zn--Fe alloy electroplated steel sheet for the purpose of manufacturing steel sheets, particularly surface-treated steel sheets for automobiles. <Prior art and its problems> Zn-Fe alloy electroplated steel sheet is a Zn-plated steel sheet with improved coating compatibility.
It has excellent corrosion resistance after painting, comparable to Zn-plated steel sheets. However, its industrial production is not easy and involves various difficulties. That is, the manufacturing method of Zn--Fe alloy electroplating which has already been disclosed, JP-A Nos. 56-9386 and 57-
No. 51283, No. 57-192284, No. 58-52493, No. 57
-200589 also had the following problems. Firstly, the plating adhesion may be poor and the plating film may peel off during processing, and secondly, Fe
There have been many problems, such as the alloy content being easily affected by the flow rate and current density, making it difficult to control the alloy content. <Object of the Invention> An object of the present invention is to provide a method for manufacturing a Zn--Fe alloy electroplated steel sheet with a beautiful plating appearance and excellent adhesion. <Structure of the invention> That is, according to the first aspect of the invention,
Contains Zn ²⁺ and Fe ²⁺ at a molar concentration ratio of 0.1≦Fe ²⁺ / (Fe ²⁺ + Zn ²⁺ )≦0.5, with a total of 0.5 mol/m ² or more within the solubility limit, and Fe ³⁺ of 1 g/m or more Using a plating bath consisting mainly of dissolved chloride, the current density is 20
Provided is a method for producing a Zn--Fe alloy electroplated steel sheet with excellent plating adhesion, which is characterized by plating at ~200 A/dm ² . According to the second aspect of the invention, Zn ²⁺ and Fe ²⁺
Contains a total of 0.5 mol/m ² or more within the solubility limit at a molar concentration ratio of 0.1≦Fe ²⁺ / (Fe ²⁺ + Zn ²⁺ )≦0.5,
Mainly chloride with 1g/or more of Fe ³⁺ dissolved, KCl, NH ₄ Cl, NaCl, as conductivity aids.
Contains 200 g or more of one or more selected from the group consisting of CaCl ₂ and MgCl ₂ , and has a pH of 2.3 to 5.0,
A Zn-Fe alloy electroplated steel sheet with excellent plating adhesion, which is plated at a current density of 20 to 200 A/dm ² using a plating bath with a bath temperature of 25 to 70°C. A manufacturing method is provided. Below, Zn-- which has excellent plating adhesion according to the present invention.
The method for manufacturing Fe-based alloy electroplated steel sheet will be explained in detail. The plating bath for Zn-Fe alloy plating mainly contains Zn ²⁺ and Fe ²⁺ ions as metal ions, which are prepared, supplied, and mixed in the form of chlorides and by dissolving metals. be adjusted. Its concentration is Zn ²⁺ and Fe ²⁺
The total amount of ions is 0.5 mol/or more, which is within the solubility limit. The reason for this is that if the total concentration is less than 0.5 mol/min, discoloration is likely to occur, while if the solubility limit is exceeded, only solids will be produced and the present invention will not have the effect of improving the plating adhesion. Fe ²⁺ /Fe ²⁺ +Zn ²⁺ is desirably 0.1 to 0.5, but this is to control the Fe content to 10 to 30 wt%. The plating bath contains KCl, NH ₄ Cl, and conductivity aids.
It is preferable to contain 200 g/or more, preferably 250 g/or more of one or more selected from NaCl, CaCl ₂ , and MgCl ₂ . The purpose of this is to stabilize the Fe content with respect to current density and flow rate, improve conductivity, reduce fading, and reduce power consumption by adding a relatively large amount. It should be noted that a chloride bath has higher cathodic deposition than a sulfate bath and also has 3 to 5 times higher electrical conductivity, so it is extremely advantageous in terms of power cost and maintaining bath balance. The current density during plating is 20 to 200 A/dm ² ,
Preferably, 60 to 150 A/dm ² is appropriate. An important feature of the present invention is that it is possible to obtain a Zn--Fe plated steel sheet with good adhesion over such a wide current density range, and a product that is stable in operation can be obtained. This is because if it is less than 20 A/dm ² , the stability of the Fe content will be poor, and if it exceeds 200 A/dm ² , it will tend to cause discoloration and may have poor adhesion. Note that the higher the current density, the better the appearance color tone becomes glossy. The relative flow velocity is preferably 30mpm or higher. This is because if the speed is less than 30mpm, discoloration will occur significantly. The bath temperature is preferably 25-70°C. This is because if the temperature is lower than 25°C, the adhesion may deteriorate, and if the temperature exceeds 70°C, the evaporation of the liquid will become more intense. PH is desirably 2.3 to 5.0, preferably 2.5 to 4.5
is desirable. If it is less than 2.3, the cathodic deposition efficiency will decrease. Therefore, it is not only disadvantageous in terms of power cost but also in terms of bath balance. on the other hand
If it exceeds 5.0, the oxidation of Fe ²⁺ becomes extremely rapid, which is disadvantageous in terms of bath balance. In addition to the above-mentioned salts, the present invention contains dissolved Fe ³⁺ which is effective in improving plating adhesion and stability of Fe content with respect to flow rate and current density. The content of Fe ³⁺ is suitably at least 1 g/, preferably at least 2 g/, more preferably at least 4 g/. If the content of Fe ³⁺ is less than 1 g/g/, the effect of improving plating adhesion and stability of Fe content is insufficient. Fe ³⁺ can be obtained by air oxidation using gas-liquid contact;
It can be supplied by oxidizing Fe ²⁺ to Fe ³⁺ using an oxidizing agent such as H ₂ O ₂ or by adding a Fe ³⁺ supplying reagent such as FeCl ₃ .6H ₂ O. By dissolving this Fe ³⁺ , it is possible to effectively improve the adhesion of plating and the ease with which the Fe content fluctuates with respect to current density and flow rate (see Figure 1). Fe ²⁺ in the Zn-Fe electroplating solution is oxidized by contact with air or dissolved oxygen to form Fe ³⁺ , but the rate of formation is slow in a chloride bath using a soluble anode. In addition, reduction of Fe ³⁺ occurs due to the chemical reaction at the anode and the electrochemical reaction during electrolysis, so the amount of Fe ³⁺ becomes almost constant on a regular basis by performing regular operations. It was found that this effect of dissolved Fe ³⁺ was particularly effective in a chloride bath to which a relatively large amount of conductivity aid was added. That is, when the concentration of conductivity aids such as KCl and NH ₄ Cl is low, the effect of improving the Fe content stability of dissolved Fe ³⁺ is small. In other words, the Fe content stability and adhesion can be improved by the synergistic effect of dissolved Fe ³⁺ and the high-concentration conductivity auxiliary agent. On the other hand, when using a sulfate bath, by lowering the pH,
Although it is possible to dissolve Fe ³⁺ ,
Fe content stability and adhesion are not sufficient. It is also known that in a chloride bath, the solubility of Fe ³⁺ in water changes depending on the pH, and the amount of Fe 3+ dissolved becomes extremely small when the pH is higher than about 2. As a result, the amount of dissolved Fe ³⁺ is about 0.5 g/or less. This is because Fe(OH) ₃ precipitate is easily generated, and the amount of dissolved Fe ³⁺ becomes smaller due to the generation of Fe(OH) ₃ . As a result, plating adhesion, Fe
The content stability becomes poor. In addition, the generated Fe(OH) ₃ precipitate adheres to the plating surface, causing plating blood defects and dent-like defects. Therefore, it is necessary to add a chelating agent to dissolve Fe ³⁺ . By chelating agent
By dissolving Fe ³⁺ , good plating adhesion and Fe content stability can be achieved. However, sulfate baths do not have the effect of improving Fe content stability or plating adhesion, but rather often lead to deterioration, such as a decrease in current efficiency, so they must be actively removed using methods such as electrolytic reduction. The reality is that The present invention improves ^plating adhesion and
The feature is that it has been found to improve the Fe content stability. In this case, in a high PH region, it is necessary to actively use a chelating agent to dissolve Fe ³⁺ . Chelating agents include those that have a larger production constant with Fe ³⁺ than with Zn ²⁺ and Fe ²⁺ , such as glycine, acetylacetone, tartaric acid, malic acid,
Succinic acid, citric acid, EDTA, thiocyanic acid,
Acetic acid, salicylic acid, sulfosalicylic acid, tyrone, etc. can be used. The addition amount may be such that Fe ³⁺ can be dissolved. As the amount of dissolved Fe ³⁺ increases, the variability of the Fe content with respect to current density and flow rate can be improved, and the Fe content becomes stable (see Figure 2). Therefore, the Fe content in Zn--Fe alloy electroplating can be stably and easily controlled. Current density and relative flow velocity are difficult to control on actual production lines, and cannot be set arbitrarily, so in order to stably control the Fe content in plating,
A major advantage is that the Fe content is highly stable with respect to current density and flow rate. That is, the present invention has made it possible for the first time to easily produce Zn--Fe plating with a uniform Fe content in the strip width direction, longitudinal direction, and between coils. Figure 3 shows the relationship between dissolved Fe ³⁺ content and plating adhesion. It can be seen that as the amount of dissolved Fe ³⁺ increases, the plating adhesion improves. It should be noted that the present invention includes the addition of a conventional brightening agent, a compound capable of brightening, or other compounds for other purposes as long as the effects of the present invention are observed. In addition, the Zn-Fe alloy plating referred to in the present invention is
Not limited to Zn-Fe alloy electroplating, Zn-Fe alloy electroplating mainly consisting of Zn-Fe, such as Zn
-Fe-P, Zn-Fe-Ni, Zn-Fe-Co, Zn-Fe
-It broadly includes Ti alloy plating, etc. <Examples> Next, the present invention will be specifically described using examples. The following experiments were conducted using a rotating cathode cell. Various tests were conducted as shown in Table 1, and the results are shown in Table 1. It can be seen that the inventive examples all have better plating adhesion and Fe content stability than the comparative examples. The test method and evaluation are as follows. (1) Plating adhesion (OT adhesion bending) With the plating surface facing outward, 180° adhesion bending was performed, and then tape peeling was performed to evaluate the amount of peeling. (2) Stability of Fe content We investigated the variability of Fe content by changing the current density and flow rate as parameters and keeping the other conditions the same. Evaluation Plating adhesion 〇No peeling, △ Slight peeling, (OT close bending) × Peeling Fe content stability 〇…0.1%/A/dm ² Within 0.1%/mpm △…0.15%A/dm ² 0.15% /mpm or less ×...0.15%A/dm ² 0.15%/mpm or more <Effects of the invention> As described above, the present invention has excellent adhesion.
Fe relationship between current density and flow velocity of Zn-Fe plated steel sheet
It can be easily manufactured while stably controlling the content. 【table】

[Brief explanation of the drawing]

FIG. 1 is a graph showing the Fe content stability of the present invention example and the comparative example, and the bath conditions are as shown in Table 1 for Example 1.
and Comparative Example 1. Figure 2 shows that the amount of dissolved Fe ³⁺ is Fe
It is a graph showing the influence on content stability,
Figure 3 shows the effect on plating adhesion. Second
The bath conditions in Figures and Figure 3 are based on Example 1 in Table 1.

Claims (1)

[Claims] 1 Zn ²⁺ and Fe ²⁺ 0.1≦Fe ²⁺ /(Fe ²⁺ +Zn ²⁺ )≦
Use a plating bath mainly composed of chloride containing 0.5 mol/m ² or more within the solubility limit at a molar concentration ratio of 0.5 and 1 g/or more of Fe ³⁺ dissolved, and a current density of 20 to 200 A/dm. ^2. A method for producing a Zn--Fe alloy electroplated steel sheet with excellent plating adhesion, which is characterized by plating in step 2. 2 Zn ²⁺ and Fe ²⁺ 0.1≦Fe ²⁺ / (Fe ²⁺ + Zn ²⁺ )≦
Contains a total of 0.5 mol/m ² or more within the solubility limit at a molar concentration ratio of 0.5, and contains chloride containing 1 g/m or more of Fe ³⁺ dissolved therein, KCl as a conductivity aid,
Containing 200 g/or more of one or more selected from the group consisting of NH ₄ Cl, NaCl, CaCl ₂ and MgCl ₂ ,
Excellent plating adhesion, characterized by plating at a current density of 20 to 200 A/dm ² using a plating bath with a pH of 2.3 to 5.0 and a bath temperature of 25 to 70°C.
A method for producing Zn-Fe alloy electroplated steel sheets.